A fuel cell is an energy conversion device that converts chemical energy of a fuel directly into electrical energy. That is, the fuel cell uses a fuel gas and an oxidizing agent, and adopts a method of producing electric power by using the electrons generated during the redox reaction of the fuel gas and the oxidizing agent. A membrane-electrode assembly (MEA) of the fuel cell is a part in which an electrochemical reaction of hydrogen and oxygen occurs, and is composed of a cathode, an anode, and an electrolyte membrane, that is, an ion conductive electrolyte membrane.
A redox flow battery (oxidation-reduction flow battery) is an electrochemical storage device that stores chemical energy of an active material directly into electrical energy by using a system in which the active material included in an electrolytic solution is oxidized and reduced and thus the battery is charged and discharged. A unit cell of the redox flow battery includes an electrode, an electrolyte, and an ion exchange membrane (electrolyte membrane).
Fuel cells and redox flow batteries have been researched and developed as a next-generation energy source due to high energy efficiency and eco-friendly characteristics producing less emission of contaminants.
The most essential constituent element of the fuel cells and the redox flow batteries is a polymer electrolyte membrane capable of exchanging cations, and the polymer electrolyte membrane may have characteristics of 1) excellent proton conductivity, 2) prevention of crossover of the electrolyte, 3) strong chemical resistance, 4) strengthening of mechanical properties and/or 4) a low swelling ratio. The polymer electrolyte membrane is classified into fluorine-based, partial fluorine-based, hydrocarbon-based, and the like, and the partial fluorine-based polymer electrolyte membrane has a fluorine-based main chain, and thus has advantages in that physical and chemical stabilities are excellent and thermal stability is high. Further, the partial fluorine-based polymer electrolyte membrane has advantages of both a hydrocarbon-based polymer electrolyte membrane and a fluorine-based polymer electrolyte membrane because a cation transport functional group is attached to the ends of a fluorine-based chain similarly to a fluorine-based polymer electrolyte membrane.
However, the partial fluorine-based polymer electrolyte membrane has a problem in that cation conductivity is relatively low because the micro phase separation of the cation transport functional group and the aggregation phenomenon are not effectively controlled. Accordingly, studies have been conducted toward securing high cation conductivity through the distribution of sulfonic acid groups and the control of the micro phase separation.